This invention relates to hydrophobically-modified polycarboxylates ("the polycarboxylates"). The polycarboxylates are novel polymers of at least two different ethylenically unsaturated carboxylic acid monomer(s) and one or more ethylenically unsaturated comonomer(s), having a C.sub.8 -C.sub.18 linear or branched alkyl chain ("hydrophobic monomer(s)"). When used as builders in liquid detergent compositions these polycarboxylates do not cause separation into different phases, thus do not require the addition of a compatibilizing agent to the detergent.
This invention also relates to a process for polymerization whereby suitable hydrophobically-modified polycarboxylates are prepared. This process unexpectedly permits solution polymerization of hydrophobically-modified monomers and carboxylic acid-containing monomers at hydrophobic monomer levels as low as 5 mole percent of the total monomers. Both the monomers and the newly formed polymer remain in solution during polymerization. Furthermore, the polycarboxylates obtained thereby have a more homogeneous distribution of all monomer units in the polymer chain than those prepared by other processes from identical starting materials. Better liquid detergent stability is achieved by the use of these homogeneous polycarboxylates.
It is well known that the selection of one polymerization process over another may affect polymer qualities as much as, if not more than, other variables, such as monomer selection, monomer ratios and the like. For example, substantially homogeneous acrylate-maleate copolymers have been prepared by controlling the rate of addition of an acrylic monomer to a solution of maleic anhydride in a chain-transfer solvent so as to maintain the monomers and newly formed copolymer in solution. U.S. Pat. No. 4,390,670, issued June 28, 1983, to Walinsky.
Furthermore, copolymers prepared by a single charge, batch process in benzene are not suited for use herein, even though these polymers are derived from comonomers which include an unsaturated carboxylic acid and acrylic esters having aliphatic chain length of 10 to 30 carbon atoms. See, U.S. Pat. No. 3,915,921, issued Oct. 28, 1975 to Schlatzer, Jr. The Schlatzer copolymers are reported to be useful primarily as thickeners for electrolyte-containing materials, including ionic detergents. The Schlatzer copolymers may comprise from 5 to 50 weight percent acrylic ester monomer. The copolymers are insoluble in benzene with the result that the copolymer is recovered by centrifuging the reaction mixture. The copolymer is preferably prepared with an additional, crosslinking monomer so as to provide maximum viscosity.
U.S. Pat. No. 3,940,351, issued Feb. 24, 1976 to Schlatzer, Jr., teaches the preparation of copolymers of an unsaturated copolymerizable carboxylic acid monomer and 10 to 30 carbon atom alkyl acrylate esters in a halogenated solvent (preferably one which is a solvent for the monomers but not for the polymer) by a single charge batch process wherein the polymer is recovered by centrifuging the reaction mixture. Maximum polymer viscosity in electrolyte-containing aqueous media is an object of the patent, and optional crosslinking monomers are preferably employed to achieve this object. The Schlatzer copolymers are compositionally and functionally distinct from the polycarboxylates prepared by the process disclosed herein. The Schlatzer copolymers are designed to thicken, whereas the polycarboxylates herein advantageously contribute little to the viscosity of isotropic liquid detergents.
Detergent compositions are generally a blend of a surfactant(s), builder(s) and, optionally, ion exchanger(s), filler(s), alkali(es), anticorrosion material(s), anti-redeposition material(s), bleach(es), enzyme(s), buffer(s), optical brightener(s), fragrance(s), solvent(s) and other components selected for particular applications.
Builders are used to improve the effectiveness of detergent compositions and thereby improve their whitening powers. The manner in which detergent builders improve the cleaning powers of detergent compositions is related to a combination of factors such as emulsification of soil particles, solubilization of water insoluble materials, promoting soil suspension in the wash water so as to retard soil redeposition, sequestering of metallic ions, and the like. Builders enhance (or "build") the cleaning efficiency of surfactants by forming complexes with hard water ions, aiding in keeping soil from redepositing on fabric being washed and buffering or moderating the pH of wash water.
Many materials are or have been used as builders in detergent formulations. Compositions and materials change frequently as formulators attempt to improve performance of cleaning while offering greater convenience in handling as well as keeping materials cost as low as possible. As heavy duty liquid laundry detergents gain market share, the need for effective non-phosphate builders which are compatible with liquid detergents becomes more acute.
Detergent builders for liquid detergents must be effective, compatible with the liquid formulation and shelf-stable. Builders which precipitate from the liquid, or cloud or gel the liquid, or cause phase separation or solid settlement initially or upon storage, are not suitable for use in liquid detergents unless an effective compatibilizing agent can be found. However, structured liquid detergents, unlike isotropic or single phase liquid detergents, generally contain builders and other components as a suspended phase, have a thick, cloudy appearance, and do not require phase compatibility. Powdered detergent formulations, which have less demanding requirements for builder compatibility and stability than liquids, can employ a greater variety of more effective builders without the need for an added compatibilizing agent.
Citric acid and its salts are used commercially as builders in liquid detergent formulations. While very compatible in liquids, the citrates do not bind calcium as effectively as the builders used in powdered detergents. Also used commercially are the liquid detergent builders comprising ether carboxylate salts (i.e., tartrate monosuccinate and disuccinate salts) which are disclosed in U.S. Pat. No. 4,663,071, issued May 5, 1987 to Bush, et al. Among the polymeric materials that have been suggested for use as liquid detergent builders are polymeric polycarboxylic acids. U.S. Pat. No. 4,797,223, which issued Jan. 10, 1989 to Amick, et al., discloses water soluble polymers with surfactant radicals distributed along a carboxylated polymer chain. The polymer may contain surfactant end groups. The surfactant radical is selected from a group of radicals having poly(alkyleneoxy) blocks characterized by a hydrophobic portion and a hydrophilic portion.
U.S. Pat. No. 4,612,352 which issued Sept. 16, 1986 to Schafer, et al., discloses water soluble or water dispersible graft polymers having at least 10 percent, by weight, of a hydrophilic graft constituent bonded to carbon and at least one hydrophobic radical bonded to the graft constituent by a polyglycol ether chain. These graft polymers contain pendant surfactant-type groups.
U.S. Pat. No. 4,559,159, which issued Dec. 17, 1985 to Denzinger, et al., discloses polymers of ethylenically unsaturated mono- and di-carboxylic acids, together with not more than 15 percent, by weight, of carboxyl-free monomers, having a terminal hydroxy radical and one or more alkylene oxide radicals.
Each of these builder compositions achieve liquid detergent formulation compatibility through the presence of pendant surfactant-type radicals on the carboxylated polymer chain. It is unexpected that liquid detergent compatibility may be achieved without employing surfactant radicals in the polymer. In place thereof, the polycarboxylates disclosed herein comprise the polymerized residue of hydrophobic alkyl ester monomers and hydrophilic carboxylic acid monomers, and are polymers having overall surfactant character.
Notwithstanding the existence of a variety of liquid detergent builders, there remains a continuing need to identify improved non-phosphorus sequestering agents, such as the unique hydrophobically-modified polycarboxylates disclosed herein.